TECHNICAL LIBRARY

Q. How do I model non standard materials, such as custom photoresists, when
using the Monte-Carlo Implant simulator in ATHENA?

A. One of the more common
questions regarding Monte-Carlo Implants, is the question of how to model a
particular type of photo resist. There are numerous
kinds in use and each have different stopping powers for ion implantation.

The
question can be expanded into how to model any user defined material that is
not in the ATHENA materials database, not just the narrower issue of photoresist.

The
physical processes of implantation have very little to do with the chemical
bonds of the target that is being implanted unless that chemistry has a direct
effect on its exact crystalline structure, such as the case in Silicon Carbide
for example. As a result, so long as the material being implanted has an amorphous
structure, it’s exact chemical bonding configuration can be ignored.
The only properties of the target which are important are :-

the fractional
abundance of each of its constituent atoms,

the atomic number of each of
its constituent atoms,

the atomic mass of each of its constituent atoms
and

the macroscopic average density of the material.

The following lines describe
how to define silicon dioxide in ATHENA as a user definable material. There
are a couple of reasons for using this as an example.
Firstly it has an amorphous structure and secondly, we can check the validity
of the user definable feature by comparing the results with the known ATHENAmaterial, silicon dioxide.

The 3 lines of the input file below show how to define
the relevant stages. The first line tells ATHENA that the material just deposited
is user defined
by the parameter “material=sand”. If “sand” was a known
ATHENA material, the syntax would be simply “sand”, not “material=sand”.

The
next statement defines the physical properties of the user defined material,
followed by a standard Monte-Carlo implant statement.

Figure 1 shows an overlay of boron
implant profiles using the above set of statements and an identical input file
using the known ATHENA material “oxide”.
The figure clearly shows identical material properties to within experimental
error.